The above glass panel is intended to enhance a thermal insulation. performance by maintaining the decompression void. defined between the glass plates in a decompressed condition. In sealing the pair of glass plates at the outer peripheries thereof, the entire glass panel is heated to a predetermined temperature to melt the sealing member provided between the outer peripheries of the glass plates. The melted sealing member is then cooled and solidified, thereby to fix the glass plates to each other at the outer peripheries thereof.
With the conventional glass panel, the entire glass panel is gradually cooled for cooling and solidifying the melted sealing member, in order to prevent internal stress from remaining in the glass plates as a result of the cooling operation and distorting the glass panel.
To this end, as schematically shown in FIG. 7, when the decompression void V in the glass panel P of FIG. 7(A) is decompressed, a strong tensile force acts on outer surfaces of the outer peripheries 9 adjacent where the glass plates 1A and 1B are sealed by the sealing member 3. As shown in FIG. 7(B), such a tensile force remains there with the decompression void V maintained in the decompressed. condition to disadvantageously generate cracks in the glass plates I due to flaws on the surfaces of the glass plates 1 or external forces applied to the glass plates 1. As a result, the decompression void V cannot be maintained in the decompressed condition for a. long period, and the glass plates 1 per se may easily be damaged.
More particularly, the above glass panel P has the glass plates 1 yielding toward the decompression void V under the pressure difference between the pressure within the decompression void V and atmospheric pressure as the decompression void V is decompressed. Since the decompression void V is decompressed with the pair of glass plates 1A and 1B fixed and bound by the sealing member 3 at the outer peripheries thereof, a strong tensile force ft remains in the outer surfaces of the outer peripheries 9 of the glass plates 1 adjacent where the glass plates are sealed by the sealing member 3 with the decompression void V maintained in the decompressed condition. Consequently, the tensile stress concentrates on flaws on the surfaces of the glass plates 1, and a resultant force of a tensile force due to an external force and the residual tensile force ft is increased, thereby tending to generate cracks in the glass plates 1.
The present invention has been made having regard to the state of the art noted above, and its object is to prevent cracks from generating in the glass plates due to flaws on the glass surfaces and external forces applied to the glass plates with the decompression void maintained in a decompressed condition.